System and method for temperature sensing

Abstract

According to an embodiment, a method of operating a measurement circuit includes biasing a sense transistor to conduct current through a first conduction channel in a first direction during a first mode, injecting a measurement current into a body diode of the sense transistor during a second mode, measuring a first voltage across the sense transistor when the measurement current is injected, and determining a temperature of the sense transistor based on the first voltage. When the measurement current is injected, it is injected in a second direction opposite the first direction. The sense transistor is integrated in a semiconductor body with a load transistor having a second conduction channel, and the first conduction channel and the second conduction channel are coupled to an input node.

What is claimed is: 
     
       1. A method of operating a measurement circuit, the method comprising:
 injecting a measurement current into a body diode of a sense transistor in a first direction during a first mode, wherein
 the sense transistor has a first conduction channel and is integrated in a semiconductor body with a load transistor having a second conduction channel, and 
 the first conduction channel and the second conduction channel are coupled to an input node; 
 
 measuring a first voltage across the first conduction channel of the sense transistor when the measurement current is injected into the body diode; and 
 determining a temperature of the sense transistor based on the first voltage. 
 
     
     
       2. The method of  claim 1 , further comprising biasing the sense transistor to conduct current through the first conduction channel in a second direction during a second mode, wherein the measurement current is injected in the first direction opposite the second direction. 
     
     
       3. The method of  claim 2 , wherein the sense transistor comprises a first control terminal coupled to a switching control input and the load transistor comprises a second control terminal coupled to the switching control input. 
     
     
       4. The method of  claim 2 , further comprising:
 providing a bias current to the first conduction channel during the second mode, wherein the first conduction channel is coupled to a sense node and the second conduction channel is coupled to an output node; 
 measuring a second voltage between the sense node and the output node during the second mode; and 
 determining a current flowing in the second conduction channel based on the second voltage. 
 
     
     
       5. The method of  claim 2 , wherein:
 injecting the measurement current comprises injecting a plurality of measurement currents into the body diode of the sense transistor during the first mode, wherein the plurality of measurement currents is injected in the first direction; 
 measuring the first voltage comprises measuring a plurality of voltages across the sense transistor when the plurality of measurement currents are injected; and 
 determining the temperature of the sense transistor comprises determining the temperature of the sense transistor based on the plurality of voltages. 
 
     
     
       6. The method of  claim 5 , wherein determining the temperature of the sense transistor based on the plurality of voltages comprises:
 providing the plurality of voltages through a floating voltage measurement circuit to a controller; and 
 calculating the temperature based on a voltage difference of the plurality of voltages. 
 
     
     
       7. A measurement circuit comprising:
 a first circuit configured to be coupled to a transistor, the first circuit configured to bias the transistor to conduct current through a first conduction channel in a first direction; 
 a controllable current source configured to be coupled to the transistor, the controllable current source configured to inject a first measurement current into a body diode of the transistor, wherein the first measurement current is injected in a second direction opposite the first direction; and 
 a temperature measurement circuit configured to be coupled to the transistor, the temperature measurement circuit configured to:
 measure a first voltage across the first conduction channel of the transistor when the first measurement current is injected, and 
 determine a temperature of the transistor based on the first voltage. 
 
 
     
     
       8. The measurement circuit of  claim 7 , wherein:
 the controllable current source is further configured to inject a second measurement current into the transistor to conduct current through the body diode in the second direction; and 
 the temperature measurement circuit is further configured to measure a second voltage across the transistor when the second measurement current is applied and determine the temperature of the transistor based on the first voltage and the second voltage. 
 
     
     
       9. The measurement circuit of  claim 8 , wherein the second measurement current is a multiple of the first measurement current. 
     
     
       10. The measurement circuit of  claim 7 , wherein:
 the controllable current source is further configured to inject a plurality of measurement currents into the transistor to conduct current through the body diode in the second direction; and 
 the temperature measurement circuit is further configured to measure a plurality of voltages across the transistor when the plurality of measurement currents are applied and determine the temperature of the transistor based on the first voltage and the plurality of voltages. 
 
     
     
       11. The measurement circuit of  claim 10 , wherein
 the transistor comprises a sense transistor having a first conduction terminal coupled to an input node, a second conduction terminal, and a control terminal coupled to a switching control input; 
 the sense transistor is configured to be coupled to a load transistor having a first conduction terminal coupled to the input node, a second conduction terminal, and a control terminal coupled to the switching control input; and 
 the sense transistor and the load transistor are integrated in a same semiconductor substrate. 
 
     
     
       12. The measurement circuit of  claim 11 , further comprising a current measurement circuit configured to be coupled to the second conduction terminal of the sense transistor and configured to be coupled to the second conduction terminal of the load transistor, wherein the current measurement circuit is configured to determine the current in the load transistor based on a voltage difference between the second conduction terminal of the load transistor and the second conduction terminal of the sense transistor. 
     
     
       13. The measurement circuit of  claim 12 , further comprising the sense transistor and the load transistor. 
     
     
       14. The measurement circuit of  claim 13 , wherein the first circuit comprises a control circuit configured to:
 during a temperature measurement mode, activate the controllable current source to inject the first measurement current into the second conduction terminal of the sense transistor, and deactivate the current measurement circuit; and 
 during a current measurement mode, activate the current measurement circuit to bias the sense transistor to conduct current through the first conduction channel, and deactivate the controllable current source. 
 
     
     
       15. The measurement circuit of  claim 14 , wherein the control circuit is coupled to the switching control input and configured to enable and disable the load transistor and the sense transistor such that the load transistor supplies a load current to a load and the sense transistor generates a sense current proportional to the current in the load transistor. 
     
     
       16. The measurement circuit of  claim 15 , wherein the control circuit comprises a microcontroller coupled to the temperature measurement circuit and the current measurement circuit, and wherein the microcontroller is configured to perform the steps of determining the temperature of the sense transistor and determining the current in the load transistor. 
     
     
       17. The measurement circuit of  claim 10 , wherein the transistor comprises a load transistor coupled between an input node and an output node and configured to conduct a load current to the output node. 
     
     
       18. A measurement circuit configured to be coupled to a conduction device comprising a sense path between an input terminal and a sense terminal, and a load path between the input terminal and an output terminal, the measurement circuit comprising:
 a controllable current source configured to inject a temperature measurement current into the sense path to conduct the temperature measurement current in a first direction during a first mode; 
 a temperature measurement circuit configured to measure a first voltage between the input terminal and the sense terminal in the first mode and generate a temperature signal based on the first voltage that is proportional to a temperature of the conduction device; and 
 a current measurement circuit configured to:
 bias the sense path to conduct a sense current in a second direction during a second mode, the second direction opposite the first direction, 
 measure a second voltage between the sense terminal and the output terminal, and 
 determine a load current in the load path based on the second voltage. 
 
 
     
     
       19. The measurement circuit of  claim 18 , further comprising the conduction device, wherein the conduction device comprises:
 a load transistor having a first conduction terminal coupled to the input terminal, a second conduction terminal coupled to the output terminal, and a control terminal coupled to a switching control input; and 
 a sense transistor having a first conduction terminal coupled to the input terminal, a second conduction terminal coupled to the sense terminal, and a control terminal coupled to the switching control input. 
 
     
     
       20. The measurement circuit of  claim 18 , wherein the current measurement circuit comprises:
 a switch having a first terminal and a second terminal coupled to the sense terminal; 
 a bias current source coupled to the first terminal and configured to supply the sense current, wherein the switch is configured to be opened in the first mode and closed in the second mode; 
 an opamp having a first input coupled to the first terminal, a second input coupled to the output terminal, and an opamp output; and 
 a measuring current source controlled by the opamp output and configured to generate a proportional measurement current that is proportional to the load current in the load path. 
 
     
     
       21. The measurement circuit of  claim 20 , further comprising
 an analog to digital converter comprising an analog input coupled to the temperature measurement circuit and configured to receive the temperature signal, and a digital output configured to provide a converted digital temperature signal; and 
 a controller coupled to the digital output and configured to calculate the temperature of the conduction device based on the converted digital temperature signal. 
 
     
     
       22. The measurement circuit of  claim 21 , further comprising:
 a transimpedance amplifier coupled to the measuring current source and configured to receive the proportional measurement current at a current input and provide a current measurement signal at a voltage output; and 
 a multiplexer coupled between the voltage output of the transimpedance amplifier and the analog to digital converter and coupled between the temperature measurement circuit and the analog to digital converter, wherein the multiplexer is configured to couple either the transimpedance amplifier or the temperature measurement circuit to the analog to digital converter, and wherein the controller is further configured to calculate the load current in the load path based on the current measurement signal. 
 
     
     
       23. The measurement circuit of  claim 20 , further comprising
 a first analog to digital converter comprising a first analog input coupled to the temperature measurement circuit and configured to receive the temperature signal, and a first digital output configured to provide a converted digital temperature signal; 
 a second analog to digital converter comprising a second analog input coupled to the measuring current source and configured to receive the proportional measurement current, and a second digital output configured to provide a converted digital current measurement signal; and 
 a controller coupled to the first digital output and the second digital output and configured to
 calculate the temperature of the conduction device based on the converted digital temperature signal, and 
 calculate the load current in the load path based on the converted digital current measurement signal. 
 
 
     
     
       24. The measurement circuit of  claim 18 , wherein the controllable current source comprises a plurality of current sources selected individually by a select signal. 
     
     
       25. A measurement circuit comprising:
 a controllable current source configured to be coupled to a first sense transistor integrated in a semiconductor body with a load transistor, the controllable current source configured to inject a first measurement current into a body diode of the first sense transistor; and 
 a temperature measurement circuit configured to be coupled to the first sense transistor, the temperature measurement circuit configured to:
 measure a first voltage across a conduction path of the first sense transistor when the first measurement current is injected, and 
 determine a temperature of the first sense transistor based on the first voltage. 
 
 
     
     
       26. The measurement circuit of  claim 25 , wherein:
 the controllable current source is further configured to inject a second measurement current into the first sense transistor to conduct current through the body diode; and 
 the temperature measurement circuit is further configured to measure a second voltage across the first sense transistor when the second measurement current is applied and determine the temperature of the first sense transistor based on the first voltage and the second voltage. 
 
     
     
       27. The measurement circuit of  claim 25 , further comprising a current measurement circuit configured to be coupled to a second sense transistor integrated in the semiconductor body with the load transistor, wherein the current measurement circuit is configured to determine a current in the load transistor based on a voltage difference between outputs of the load transistor and the second sense transistor. 
     
     
       28. The measurement circuit of  claim 25 , further comprising the first sense transistor and the load transistor, wherein the load transistor has a width that is more than 1000 times greater than a width of the first sense transistor.